Hello,

I want to measure the pressure on a 4-wire resistive touch panel (8") with an Uno board. I am using A0 to A3 pins which are switched between input and output states to measure x, y, z1 and z2 values

There are two formulas one can found in many datasheets (see picture below) to calculate the pressure (z or R_{touch}) but I can't find any real example. I have tried the first formula. However I can't get a pressure value which is not correlated to the xy position.

First I am not sure to have the right figure for the R_{x_plate}. I have measured the panel's resistance when left unpowered but maybe it's not how one should do it ? I have also tried some random values for R_{x_plate} but it doesn't seem to reduce the correlation between the position and the pressure.

I am also wondering whether the actual values I get from the ADC might demand some kind of correction in the formula if those values do not reach the digital scale's extremes (0 and 1023).

Is the second formula better or should I use another way to measure the pressure ?

Second, I am not sure about the additional components I should use besides the panel and the Arduino. In some circuits people use pull-up resistors, others do use pull-down resistors, other talk about capacitors, ESD diodes. Currently I am using 10k pull-down resistors but is there a better design (to use the whole ADC's range for instance) ?

Third, in some controller's datasheets one can read about differential or ratiometric vs single-ended reference for the ADCs. Does this has any importance when using an Arduino board ?

Any help would be much appreciated.